The present invention relates to a novolac-epoxy resin foam, a method for making a novolac-epoxy resin foam, and a foamable composition for forming a novolac-epoxy resin foam.
Phenolic resin foams are well known and provide many advantages over polyurethane foams. For example, polyurethane foams produce many toxic fumes when burned, whereas phenolic foams produce significantly less toxic fumes when burned. Phenolic resin foams are usually formed from a resol resin, as described in my U.S. Pat. Nos. 5,616,626 and 5,693,684, the complete disclosures of which are incorporated herein by reference. Resol resins are formed by reacting phenol based compounds with an aldehyde. Linear resol resins are commonly known as novolac resins.
Polyurethane foams can be easily be formed having a closed-cell structure. A closed-cell structure is understood as the ability of the cell wall to inhibit the outward diffusion of trapped blowing gas and the inward diffusion of air. Such closed-cell polyurethane foams can be produced under atmospheric pressure. In contrast, conventional phenolic resin foams must be produced under high pressure to form such a closed-cell structure. U.S. Pat. No. 4,423,163 describes such a high pressure method for making a closed-cell phenolic resin foam, in which the foam is produced under about 6 psi. The requirement of pressure for making a closed-cell phenolic foam results in significant disadvantages and is not commercially feasible, especially when compared to closed-cell polyurethane foams that can be produced under atmospheric pressure.
My U.S. patent application Ser. No. 09/070,765, the complete disclosure of which is incorporated herein by reference, discloses a method for forming closed-cell phenolic resin foam, which utilizes a bond strength enhancing agent so that the foam can be formed under ambient pressures.
There is a need for other methods of making closed-cell phenolic resin foams that do not require the use of pressure greater than atmospheric. There is also a need for an adjustable, phenolic based foam system which can be adapted to be sprayable, to provide various levels of closed and open cells, to provide different levels of flexibility, and to meet local residential and commercial building flamability codes.
Spray foaming is a process in which two or more reactive components are mixed, such as in a mixing head, where they begin to react. The resulting reaction mixture is then sprayed onto a surface where the mixture foams and cures, thereby forming a cured foam layer on the surface. A mixing head suitable for use in carrying out spray foaming is described in U.S. Pat. No. 4,332,335, which is incorporated herein by reference. The head consists of a mixing chamberwhich communicates with a discharge orifice and first and second ducts which dispense the reactive components into the mixing chamber. Means are provided for regulating the flow of the reactants to the reaction chamber.
To be suitable for spraying, the foam-forming composition must have a low viscosity. For spraying on vertical surfaces the foam-forming composition must also have a fast cure speed to prevent gravity-induced sagging or running of the foam. Therefore, spraying methods have been used primarily for foam-forming compositions consisting of polyurethane and polyisocyanate resins, which have the combination of a low viscosity and a fast cure rate. However, foam-forming compositions based on polyurethane and polyisocyanate produce a polyurethane foam having an undesirably low temperature resistance, which significantly limits the use of polyurethane foams. For example, insulation for use in residential homes, commercial buildings, foundries, automobiles, boats, and wherever high temperature insulation is required, must have a temperature resistance significantly greater than that of polyurethane foams. The temperature resistance of the polyurethane foam can be increased slightly by using additives. However, such additives have many undesirable effects on the properties of the foam. Furthermore, when polyurethane foams are burned they undesirably produce fumes which are very toxic to humans.
Foams made from phenolic resins have a temperature resistance significantly greater than polyurethane foams. Furthermore, foams made from phenolic resins do not produce toxic fumes when burned. However, known foam-forming, phenolic resin compositions have not previously been used in spraying methods because they exhibit undesirably slow curing rates, the viscosity of the phenolic resin composition is undesirably high for spray applications, and chemical blowing agents must be added to produce the foam. Use of chemical blowing agents, such as chlorofluorocarbons, are undesirable because they are environmentally unfriendly. Thus, there is and has been a need for a sprayable, foam-forming composition having the combination of properties of (a) not requiring the use of an external blowing agent, (b) having a viscosity suitable for spraying, (c) having a suitably fast curing rate, and (d) when suitably cured providing a foam having a high temperature resistance and which does not produce toxic fumes when burned.
My U.S. Pat. No. 5,693,684 discloses a sprayable , foam-forming phenolic resin composition. Resol resins are utilized, preferably in combination with a phenol compound. This patent does not specifically disclose the use of epoxy resins in combination with novolac resins.
U.S. Pat. No. 4,291,146 discloses a heat-curable mixture of epoxide resins and beta-aminocrotonic acid derivatives. This patent discloses that the epoxy formulations may be used to form foams. Use of a glycidylised phenol novolac resin having epoxide equivalent weight of 175 is disclosed in the examples. However, this patent does not disclose reacting an epoxy resin with hydroxyl groups present on a novolac resin while blowing to form a foam, nor a flexible system of providing different levels of flexibility in the cured foam by adjusting the ratio of epoxy resin to novolac resin. This patent also does not disclose a foam that is suitable for spraying.
There is a need for an adjustable, foam-forming system to provide varying levels of foam flexibility, a neutral pH to avoid corrosion, and which can be adapted to be sprayable. There is also a need for a flame-retardant foam which does not produce toxic fumes when burned.
The above objectives and other objectives are achieved by the novel combination of a novlac resin and an epoxy resin to provide foams. The flexibility of the foam can be easily increased by increasing the amount of novolac resin compared to the amount of epoxy resin. The foam forming composition can easily be adapted for spraying applications.
The present invention provides a novel foamable composition adapted to form a cross-linkednovolac-epoxy resin foam. The foamable composition is formulated from a composition comprising at least one novolac resin, at least one epoxy resin, and at least one blowing agent.
The present invention also provides a flame-retardant, foamable, novolac-epoxy resin composition. The foamable composition is formulated from a composition comprising at least one novolac resin, at least one epoxy resin, at least one blowing agent and at least one flame retardant.